pfil: avoid disclosing uninitialized data in pfil ioctls

[chs]

Summary

Use M_ZERO when allocating the temporary memory in pfilioc_listheads()
and pfilioc_listhooks(). these buffers are not necessarily completely
initialized before being copied out to userland.
Found with KMSAN.

Sponsored by: Netflix
Assisted-By: Claude Code - Opus 5 (1M context)

[glebius]

Thanks!